Ultrasound equipment may be used for measuring the velocity and other characteristics of blood flow, by using Doppler color mode processing for diagnostic imaging. Unfortunately, the signals of interest often have lower amplitudes than signals from other objects within the same imaging field. Such signals, which include reflections from large, stationary objects or even large, slow-moving objects, are often not of interest in Doppler color mode processing. These unwanted signals are called clutter signals, and color mode processing detection must often discriminate against such clutter signals.
Filters are generally used to reject clutter signals, which then allows detection of relatively weak signals of interest. Clutter rejection filters, however, should pass the signals of interest without undue attenuation. Since a relatively small number of samples may be used in Doppler color mode processing, the transient response of the filters must be carefully controlled. For example, a typical system may attempt to estimate blood velocity with only 8 to 16 ultrasound pings. This provides challenges in designing a filter that effectively discriminates between large stationary signals and the small signals of interest. If the filter is ill-suited to the specific application, it may either fail to block enough clutter, or else block the signals of interest.
Previous solutions include using a single filter for all anatomical regions. Although the filters have been theoretically optimized for desirable mathematical properties, they may not be truly optimum for all applications. Typical solutions use a two-dimensional (2D) matrix filter, and attempt to minimize the transient response. One possible approach is described by Dustin E. Kruse & Katherine W. Ferrara, A New High Resolution Color Flow System Using an Eigendecomposition-Based Adaptive Filter for Clutter Rejection, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 49, No. 12, Dec. 2, 1739-1754, the entire disclosure of which is hereby incorporated by reference.